richardash1981 Posted June 14, 2015 Share Posted June 14, 2015 I'm trying to "fix" the induction loop installation at a local church. The original installation (a long time ago) was an ILD9 with a single turn loop about 5m up the walls, signal tapped off the 100V PA line via Ampetronic's adaptor for the purpose. The PA system has since been replaced (with what might be a low impedance speaker system), and the loop was reported as "not working". Apart from a mess getting signal to the amp, the amp showed no signs of life when switched on at the mains (it seems to have been left on 24/7 for years). The loop itself is intact, and hooking up a spare ILD9 unit of mine produces an OK signal strength (on field strength meter), although it does need to be turned pretty much all the way up (occasional flashes of the red 9.6A LED). One way or another the input can be sorted - for these tests a separate signal cable was run. I then took the Church ILD9 home for a bit more of a look. The 1.6AT mains fuse is blown, and quite violently - metal all over the inside of the glass tube. When I changed this and powered up from a variac, it drew > 2A at 40V AC - so I switched it off quick! There is no sign of anything burnt inside the box. I tried disconnecting the mains transformer secondary, and that works fine - draws no current, correct secondary voltages. So it's something on the PCB which is drawing all the current, and as the PSU caps look OK, the output transistors are the most likely culprit. When I looked up the output transistor data sheet, I find that the transistors now in the output stage have 2007 date codes on them, so they have been replaced before (presumably because they needed it). So I now have the question: why did the installed amp fail, and is the replacement likely to do the same? I was under the impression that an ILD9 was fairly indestructible, in that it does a loop test on switch-on and has over-temperature and overdrive protection, but maybe there is something problematic about the load? The original amp is an Issue 2 PCB (which has a number of modifications to it), the replacement is Issue 4 and dates from 2000 (transformer and transistor date codes). Link to comment Share on other sites More sharing options...
Shez Posted June 14, 2015 Share Posted June 14, 2015 What do Ampetronic themselves say? They're very helpful in my experience. Link to comment Share on other sites More sharing options...
Jivemaster Posted June 14, 2015 Share Posted June 14, 2015 Seconded try Ampetronic, Don't be surprised if the installers of the low impedance system changed, altered or even damaged the system. Link to comment Share on other sites More sharing options...
bruce Posted June 14, 2015 Share Posted June 14, 2015 I know it’s not the answer you’re looking for, but 3 of these units have sold recently on Ebay - the cheapest for 25 pounds, the dearest 75. Probably not worth spending too much time on it. Link to comment Share on other sites More sharing options...
pstewart Posted June 14, 2015 Share Posted June 14, 2015 3rded to try Ampetronic. Also, you've probably checked, but the loop is well insulated from earth isn't it? For reference on an ILD9 there's an insert loop on the back - the jack sockets on that can need cleaning, or a patch lead to join them also fixed my no audio problem :-) Link to comment Share on other sites More sharing options...
Simon Lewis Posted June 15, 2015 Share Posted June 15, 2015 Check the things mentioned so far - loop impedance, continuity and isolation from earth. There must be something wrong if you are having to drive it hard with little output? If you don't mind connecting your unit up again, try driving a test signal into it whilst the PA is switched on. Can the test signal be heard in the PA? If so, there may well be magnetic feedback between the loop and the PA which will need sorting out before you put any loop map back in there. Ampetronic do a fixed price repair for the ILD9 - about £60. They are also very helpful indeed on the phone... Simon Link to comment Share on other sites More sharing options...
richardash1981 Posted June 18, 2015 Author Share Posted June 18, 2015 Check the things mentioned so far - loop impedance, continuity and isolation from earth. There must be something wrong if you are having to drive it hard with little output? If you don't mind connecting your unit up again, try driving a test signal into it whilst the PA is switched on. Can the test signal be heard in the PA? If so, there may well be magnetic feedback between the loop and the PA which will need sorting out before you put any loop map back in there.Thank you for all the information - certainly some things to work on. Ampetronic have confirmed they saw the Church amplifier for repair in 2005 and 2008, so it seems to have been trouble for a while - definitely more loop tests. I hadn't thought of magnetic feedback, so far it has only been run with the installed PA system switched off. Their general view is "7 years for this amplifier isn't too bad!I don't think the change of input signal or problems with the loop will have contributed to the problem, it is much more likely to simply be component failure due to time and constant use." I'm not sure I quite buy this, because as a designer, I don't expect transistors to wear out! I'm well aware another second hand unit will be cheaper than repair - but don't want to need another one every 3 years! The loop area is 16m by 9m rectangular (144m^2) so not a trivial drive, but I take the point it shouldn't need to be flat out. I wonder if it is cross-connected with the PA system speaker wiring - they do share a junction box ... Link to comment Share on other sites More sharing options...
timsabre Posted June 18, 2015 Share Posted June 18, 2015 Have you meggered the loop wiring to earth? Our church induction loop started to give problems, I borrowed a proper high voltage insulation tester and found multiple places where the loop was earthed due mostly to split insulation and damp areas. Link to comment Share on other sites More sharing options...
richardash1981 Posted June 18, 2015 Author Share Posted June 18, 2015 Have you meggered the loop wiring to earth? Our church induction loop started to give problems, I borrowed a proper high voltage insulation tester and found multiple places where the loop was earthed due mostly to split insulation and damp areas. No - it got a check with a multimeter, but sounds like I need to borrow work's Megger and do this properly! Link to comment Share on other sites More sharing options...
Bazz339 Posted June 19, 2015 Share Posted June 19, 2015 Have you meggered the loop wiring to earth? Our church induction loop started to give problems, I borrowed a proper high voltage insulation tester and found multiple places where the loop was earthed due mostly to split insulation and damp areas. No - it got a check with a multimeter, but sounds like I need to borrow work's Megger and do this properly! I would check as thoroughly as you can that the loop wire isn't connected to anything it shouldn't be first and if possible use something that can test the insulation at a safer voltage first, say 25V or 50V, my Multifunction installation tester will do that, can't remember what the PATester goes down to but it is useful for putting a high current (10 or 30A) through the loop and measuring resistance. Link to comment Share on other sites More sharing options...
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